1. Field of the Invention
The present invention generally relates to a sliding exhaust brake system which is connected to the exhaust pipe of a large-sized vehicle such as a truck or bus and closes off the exhaust gas discharge passage in the exhaust pipe to brake the vehicle when it goes down a steep hill. More particularly, the invention relates to improvements in the structure of the sliding exhaust brake system.
2. Description of the Prior Art
A conventional valve mechanism used in an exhaust brake system of this kind is shown in FIG. 3, where a valve member 23 takes the form of a flat plate and is provided with an exhaust pressure-adjusting hole 24 in its bottom wall. The valve member 23 is mounted in a housing 21 forming the body of the exhaust brake system. An auxiliary valve member 30 consists of a liner 29 sliding on the surface of the valve member 30 together with a support frame 28 over which the liner 29 fits. The frame 28 is mounted to the front end of a piston rod 26 via a block member 25. The valve member 23 engages the rod 26 which extends through the partition wall of an actuator such as a cylinder device 22 or a diaphragm device connected with the body of the brake system. The exhaust gas passage is closed off after the exhaust pressure-adjusting hole 24 is closed by the auxiliary valve member 30. The passage is opened after the adjusting hole 24 is opened.
In recent years, the output powers of internal combustion engines of automobiles have been increased more and more, and an increasing number of engines are supercharged. That is, engines have tended to be rotated at higher speeds. Therefore, the present situation is that the exhaust pressure and the amount of exhaust gas tend to be increased. With the conventional mechanism described above, however, since the exhaust pressure increases, the obtained smoothness, especially responsiveness, tends to be insufficient especially when the exhaust passage is closed. In particular, in order to close off the passage, the exhaust pressure-adjusting hole 24 is first closed by the auxiliary valve member 30. Under this condition, the valve member 23 is moved to close off the exhaust passage. As a result, the aforementioned undesirable phenomena tend to occur. To avoid these problems, the actuator has had to be made larger.